An optical heterodyne receiver for ASK- and DPSK-modulated signals is described in "Electronics Letters," Sept. 12, 1985, Vol. 21, No. 19, pp. 867-868. The two input ports of a 2.times.2 fiber coupler are presented with linearly polarized light and circularly polarized light, respectively, and one of the output ports of the coupler is connected to a polarization-selective beam splitter delivering two light signals in quadrature which, after separate optical-to-electric conversion and demodulation, are added together to form a useful signal. To improve the sensitivity of the receiver, an automatic polarization controller is proposed which is independent of the receiver (see FIG. 1 of the cited article).